1. Field of the Invention
This invention relates to semiconductor materials and methods of forming the same, and more particularly to .beta.-silicon carbide semiconductors.
2. Description of the Related Art
Silicon has gained acceptance as the basic semiconductor material, with other semiconductors such as GaAs used for limited applications such as extra high speed operations. However, both silicon and GaAs have significant limitations in terms of voltage breakdown levels, saturated electron drift velocity and the density of devices that can be implemented with these materials. Furthermore, it is not practical to make heterostructure devices with silicon, and both silicon and GaAs have fixed bandgaps that cannot be changed for different applications.
A new type of semiconductor referred to as beta silicon carbide(.beta.-SiC) has been developed recently which generally retains the operating features of more conventional semiconductors, but has significant advantages. As compared with both silicon and GaAs, .beta.-SiC exhibits a very high breakdown voltage, a high saturated electron drift velocity which makes it useful for extremely high frequencies, and a high thermal conductivity which aids in heat dissipation and a consequent capability for a very high density of devices. In addition, the wide bandgap and superior high electric field properties of .beta.-SiC, in conjunction with advances in submicron semiconductor processing technology, offer the possibility of significant breakthroughs in size, power, speed, operating temperature and radiation resistance of solid state semiconductor devices and integrated circuits. This new semiconductor and its potential applications are described in J. D. Parsons, R. F. Bunshah and O. M. Stafsudd "Unlocking the Potential of Beta Silicon Carbide", Solid State Technology, November 1985, pages 133-139.
While .beta.-SiC has very significant advantages that make it a potential replacement for silicon as the basic semiconductor, it also has some limitations. Like silicon, its bandgap is fixed and prevents it from being used for several types of devices such as high electron mobility transistors (HEMT), avalanche photo diodes (APD), heterojunction bipolar transistors, impact avalanche transit time diodes (IMPATT) with narrow bandgap avalanche regions, and bandfolded superlattices for infrared detectors and lasers. Furthermore, .beta.-SiC has a low low-field mobility which reduces maximum operating frequency of a metal-semiconductor-field effect transistor (MESFET) near the source and drain contact.